Polymorphism in the human arylamine N-acetyltransferase 1 gene 3'-untranslated region determines polyadenylation signal usage

Human arylamine N-acetyltransferase 1 (NAT1) encodes a drug-metabolising enzyme that plays a role in chemical-associated cancer risk, cancer cell survival and mitochondrial function. Its expression and protein activity are regulated by transcriptional, translational, and post-translational processes, including microRNAs such as miR-1290. Several studies have shown the presence of multiple polyadenylation sites in the NAT1 gene. However, their role in NAT1 expression is poorly understood. Here, we have investigated the genetic sequence of the NAT1 gene in human cell lines, peripheral blood mononuclear cells and breast tumour tissue. We identified five potential polyadenylation signals, two of which carry known single nucleotide polymorphism that affect site usage. Cells that are homozygous for adenine at base 1642, the most distal polyadenylation site, use this site whereas those homozygous for cytosine at base 1642 could not. We also found that the presence of adenine at base 1642 is associated with the NAT1*10 haplotype. Because the putative binding site for miR-1290 is located between the last two polyadenylation sites, we hypothesised that cells that do not use the most distal site will be unaffected by miR-1290. However, this was not the case. NAT1 activity was positively correlated with miR-1290, and induction of miR-1290 in SH-SY5Y cells was associated with induction, not inhibition, of NAT1 activity. The use of PolyA¹²⁶⁴ or PolyA¹⁶⁴² did not alter NAT1 activity following ectopic expression of a miR-1290 mimic. These results suggest that the role of miR-1290 in the regulation of NAT1 activity is more complex than previously reported.